Cement, such as Portland cement, is a very widely-used material in the field of construction. However this cement, although it is of high performance, requires, for the manufacture thereof, on the one hand, the consumption of many resources and, on the other hand, produces a non-negligible quantity of pollutants that are responsible, among others, for climate warming and acid rain. Finally, its service life, although long, is limited by the multiple degradations, in particular linked to atmospheric pollution, that it can be subjected to over time. All of these particularities make Portland cement increasingly less present in a sustainable development approach.
There are alternatives to conventional construction materials but they only partially meet the necessary performance requirements. In addition, their high economic cost is often a limit for large use.
For example geopolymers were invented around the end of the 1970's by Professor Davidovits. Their properties in terms of durability, mechanical performance and sustainable development have recently brought these new generation binders to stage front.
A geopolymer is formed from a mineral matrix comprised of silica and of alumina having reaction sites whereon cross-linking agents are made to react contained in a solution referred to as activating, generally alkaline. This reaction produces a gel with a poly(silico-oxo-aluminate) base which coats the granulates and hardens as the reaction progresses, until monolithic block is obtained comprised of a “glass” wherein the granulates are covered. However the methods for producing these geopolymers are either hardly adaptable industrially and/or use expensive products. The reactions are generally carried out with a heating of the constituents.
An example of manufacturing at ambient temperature of geopolymeric cement with a silico-aluminous fly ash (referred to as class F) is described in patent EP 2061732 B1 of J. Davidovits. However the base material, the silica-aluminous fly ash (referred to as class F), coming from coal-fired power plants, is a material that is not widely available in France.
In another more recent patent application FR 2966823 of the same inventor is described a method for manufacturing a binder or geopolymer cement comprising a first step of treatment of geologic elements rich in iron oxides and in ferro-kaolinite at a temperature from 600 to 850° C. for several hours, during which the ferro-kaolinite becomes ferro-metakaolin, then in a second step of having them react with a reaction medium of the Ca-geopolymeric type at ambient temperature or less than 85° C. The examples of this document indicate that the geopolymeric precursor which here is ferro-metakaolin is prepared during a long thermal treatment (calcination at 750° C. for 3 hours, followed by crushing) and therefore consume a substantial amount of energy.
Moreover document US 2012/0192765 A1 presents formulations of geopolymer based on a metakaolin M1200S produced according to the flash furnace AGS method. The calcination characteristics are indicated in the patent as being a temperature chamber 900 to 1000° C. bringing the kaolin to 750 to 850° C. for a very short period of time (not precisely indicated in this text).
This metakaolin M1200S has a high reactivity but its flash calcination mode produces a very fine metakaolin (paragraph [0024] indicates a D50 between 1 and 2 μm) having in particular a very high water demand (1650 g/kg in the Marsh funnel, according to the technical sheet). The required quantity of activation solution is therefore notoriously high: in particular a (M2O+SiO2)/matrix ratio of 11.3 mol/kg (for the formulation “ex1”) and of 10.6 mol/kg with a substantial use of superplasticiser (for the formulation “ex14”), (see the comparative tables further on).
However, the activation solution, containing soda and sodium silicate, represents a substantial proportion of the economic cost and of the environmental impact. As such the production of a tonne of soda requires more than 20 MJ of energy and 1.3 T eq CO2 of a carbon footprint responsible for climate warming. In addition, soda represents, due to its substantial corrosivity, the most dangerous constituent in the formulations of geopolymers. Finally, the activation solution, through its content in saline elements is responsible for the efflorescence effects observed in geopolymers. It is therefore suitable to limit the quantities of activation solutions in the formulations to a minimum.
This invention has for purpose to overcome the disadvantages of prior art by proposing a composition for a construction material from materials that are easily available and reactive, and with a low ecological impact: in particular that do not require any long and expensive thermal treatment.
Another purpose of the invention is to propose a composition for a construction material with a reduced quantity, and even an absence of cement or clinker, that can be used for the confection of various construction modules or elements, by moulding or extrusion.
Another purpose of the invention is to propose a composition for a construction material that can be implemented in a method for manufacturing construction modules or elements in a mixture with unfired clay, without requiring firing.